Considering the recent rapid progress of the information communication industry, the amount of data, such as transaction information and data for homepages, which is communicated on a communication network represented by the Internet, is expected to drastically increase in the near future. In order to cope with such drastic increase in the data amount, a mass storage apparatus is in great demand.
As an information storage apparatus which has gotten a lot of attention recently, there is an optical information storage apparatus that stores information by means of an optical storage medium represented by an MO, a DVD and the like. Such an optical information storage apparatus is required to have a drastically increased capacity to cope with the drastic data amount increase expected in the near future. As techniques for achieving a mass-storage capacity of the optical information storage apparatus, there have been proposed utilization of a blue laser diode as a light source for recording and reproduction on and from an optical storage medium, recording to both sides of a disk-like optical storage medium, increase of NA in the objective lens of a recording head, and the like.
Among these techniques, the increase of NA in the objective lens of a recording head is an effective technique to achieve a mass-storage capacity of an optical information storage apparatus. However, the increase of NA in the objective lens causes the following problem.
For example, if NA in the objective lens is increased without changing the aperture of the objective lens, the focal distance of the objective lens is shortened. In such a case, it is necessary to bring the recording surface of an optical storage medium close to the objective lens. As a result, it is inevitably required to make the gap between the optical storage medium and the objective lens shorter and furthermore to make the thickness of the medium protection film covering the recording surface of the optical storage medium thinner. For example, in the case of a generally distributed optical information storage apparatus that stores information in a CD, the gap between the CD and the objective lens is 1 mm or more, and the thickness of the medium protection film of the CD is about 1.2 mm. On the other hand, if NA in the objective lens is increased as described above, the gap between the optical storage medium and the objective lens is as short as 0.1 mm or below, and the medium protection film of the optical storage medium is as thin as 0.1 mm or less. For example, if dust adheres to the surface of the medium protection film, this causes a possibility that the dust may intercept the path of light irradiated from the recording head and focused on the recording surface. If the medium protection film is thin, the surface of the medium protection film is close to the focal point on the recording surface. Therefore, on the surface of this medium protection surface, the light emitted from the recording head is sufficiently narrowed by the objective lens. As a result, even if the size of the dust adhering to the surface of the medium protection film is very small, a part intercepted by the dust, of the light transmitted through the surface of the medium protection film is large. Furthermore, when the gap between the optical storage medium and the objective lens is short, if a relatively large-sized piece of dust is allowed to go to the vicinity of the gap, it may happen that the dust stays between the optical storage medium and the objective lens, intercepts the light emitted from the recording head for a long time and gives serious damage to reading and writing of information from and on the optical storage medium. Thus, the increase of NA in an objective lens may cause a problem that the resistance against dust adhering to the optical recording medium and the objective lens is reduced.
In order to cope with such dust, there have been proposed a technique of cleaning an optical system and a carrying system with the use of a cleaning disk (see Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5 and Patent Document 6, for example), a technique of providing a drive for cleaning in parallel with a drive for recording and reproduction to clean an optical storage medium (see Patent Document 7 and Patent Document 8, for example), and so on.
(Patent Document 1)
Japanese Patent Laid-Open No. 13-93121
(Patent Document 2)
Japanese Patent Laid-Open No. 5-54513
(Patent Document 3)
Japanese Patent Laid-Open No. 5-74127
(Patent Document 4)
Japanese Patent Laid-Open No. 5-114155
(Patent-document 5)
Japanese Patent Laid-Open No. 7-235120
(Patent Document 6)
Japanese Patent Laid-Open No. 12-57077
(Patent Document 7)
Japanese Patent Application No. 5-74127
(Patent Document 8)
Japanese Patent Application No. 5-114155
However, as shown in the Patent Documents 1 to 8, there is a problem that, if a cleaning mechanism is provided within an optical information storage apparatus, the size of the apparatus is large. Furthermore, there is also a problem that the optical storage medium may be damaged due to an unexpected accident caused by providing such a cleaning mechanism.